Reception apparatus and reception method

ABSTRACT

A receiving apparatus includes an amplification section that amplifies a received signal and a frequency conversion section that converts a frequency of the received signal, from a radio frequency to a baseband, the baseband having a lower frequency than the radio frequency. A gain control section amplifies, by a predetermined gain, the signal that has been subjected to the frequency conversion to the baseband. A voltage calibration section performs calibration on an offset voltage generated in the signal subjected to frequency conversion to the baseband. A time constant control section sets a first time constant during a reception operation and sets a second time constant, which is reduced with respect to the first time constant, during the calibration. A filter section passes a received signal of a predetermined band, with the first time constant or the second time constant, an operation control section stops operation of the amplification section during the calibration, controls the amplification section to operate during the reception operation, and controls the operation of the amplification section so as to reduce a residual offset voltage caused by switching the operation of the amplification section.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of pending U.S. patent applicationSer. No. 10/581,451, filed Jun. 1, 2006, which is a National Stage ofPCT/JP04/017784, filed Nov. 30, 2004, which is based upon JapaneseApplication No. 2003-402231, filed Dec. 1, 2003 the disclosures of whichare expressly incorporated herein by reference in their entireties. TheInternational application is not published in English.

TECHNICAL FIELD

The present invention relates to a reception apparatus and receptionmethod, and more particularly, to a reception apparatus and receptionmethod for calibrating an offset voltage of a received signal.

BACKGROUND ART

In recent years, as a means of realizing a smaller and multiband radioterminal at lower cost, a direct conversion reception scheme is becominga focus of attention and a portable terminal mounted with a directconversion reception apparatus is becoming the mainstream.

However, a widely known disadvantage of the direct conversion receptionapparatus is a DC offset voltage (hereinafter “offset voltage”). Thatis, in the low-frequency part of the baseband frequency band after anquadrature demodulator, it is not possible to implement capacitycoupling given the stabilization time after start-up of a receiver, andtherefore an offset voltage of the quadrature demodulator output whichis produced due to the fact that the local oscillating frequency at aninput terminal of the quadrature demodulator and the input signalfrequency are identical, is output multiplied by a gain of thelow-frequency part, which causes circuit saturation in the low-frequencypart and degradation of reception sensitivity.

Conventionally, there is an offset voltage calibration scheme, wherebyan offset voltage calibration start signal is received from a digitalsignal processing section, the time constant of a low pass filterconstituting an analog baseband circuit (low-frequency part) is reducedso as to realize high accuracy and high speed of offset voltagecalibration at the same time (for example, see Patent Document 1).

FIG. 1 shows conventional reception apparatus 10. In FIG. 1, receptionapparatus 10 is constructed of: variable gain amplifier 11; offsetvoltage calibration circuit 12 for variable gain amplifier 11; low passfilter 13; resistors 14 and capacitor 15 constituting low pass filter13; switches 16 that separate capacitor 15 from signal wiring; analogbaseband circuit 17 composed of variable gain amplifier 11 and low passfilter 13; digital signal processing section 18 that converts a signalreceived from analog base band circuit 17 to an audio signal or datasignal and transmits an offset voltage calibration start signal tooffset voltage calibration circuit 12; low noise amplifier 19;quadrature demodulator 20; and decoder 21.

A high-frequency signal received by an antenna (not shown) is amplifiedby low noise amplifier 19 and then distributed to two routes. A carrierhaving substantially the same frequency as the above high-frequencysignal is supplied from a local oscillator (not shown). The abovecarrier, which is divided into two signals having a phase difference of90 degrees by a phase shifter and the above high-frequency signal aremixed by quadrature demodulator 20 and frequency-converted to a basebandfrequency band. The baseband signal is amplified by variable gainamplifier 11 and frequency-selected by low pass filter 13 and output todigital signal processing section 18.

When triggered by the offset voltage calibration start signaltransmitted from digital signal processing section 18, this receptionapparatus 10 opens switch 16 and starts the operation of offset voltagecalibration circuit 12.

Furthermore, there is another conventional offset voltage calibrationscheme, whereby a high-frequency block is always kept in a non-operatingstate during the offset voltage calibration operation and improvesresistance against interferer (for example, see Patent Document 2).

FIG. 2 shows conventional reception apparatus 30. In FIG. 2, receptionapparatus 30 is constructed of: antenna 31; low noise amplifier 32;local oscillators 33, 36 43; mixers 34, 37, 41, 42; bandpass filters 35,39; switch 38; variable gain amplifier 40; phase shifter 44; A/Dconverters 45, 46, 50; offset voltage calibration circuits 47, 48; logamplifier 49; carrier detection circuit 51; and control circuit 52.

A high-frequency signal received by antenna 31 is amplified by low noiseamplifier 32 and then converted to a first intermediate frequency bylocal oscillator 33, mixer 34 and band pass filter 35. The signal isfurther converted to a second intermediate frequency by local oscillator36, mixer 37, bandpass filter 39 and then distributed to two routesthrough variable gain amplifier 40. The signal is then mixed with acarrier having substantially the same frequency as the secondintermediate frequency supplied from local oscillator 43 at mixers 41,42 and frequency-converted to a baseband frequency band.

In such reception apparatus 30, control circuit 52 generates controlsignals for switch 38, offset voltage calibration circuits 47, 48, basedon a frame synchronizing signal output from a digital signal processingsection (not shown). During the offset voltage calibration operation byoffset voltage calibration circuits 47, 48, switch 38 is open so thatmixer 37 is in a non-operating state and the leakage of interferer tomixer 37 and subsequent circuitry is reduced.

Furthermore, there is yet another conventional offset voltagecalibration scheme, whereby a high-frequency block is kept in anon-operating state during the offset voltage calibration operation,thereby improving resistance against interferer, and whereby animpedance compensation circuit is provided additionally to suppress theresidual offset voltage produced due to the fact that the high-frequencyblock operating state differs between the time of calibration operationand the time of reception operation (see, for example, Patent Document3).

FIG. 3 shows conventional reception apparatus 60.

In FIG. 3, reception apparatus 60 is constructed of: high-frequencyblock 61; power supply 62 for high-frequency block 61; baseband signalprocessing block 63; quadrature demodulator 64; impedance compensationblock 65; antenna 66; first local oscillator 67; phase shifter 68;second local oscillator 69; quadrature modulator 70; phase shifter 71;third local oscillator 72; offset voltage detection block 73; offsetvoltage calibration control block 74; bandpass filter 75; limiteramplifier 76; and demodulator 77.

During the offset voltage calibration operation of baseband signalprocessing block 63, bias supply from power supply 62 to high-frequencyblock 61 is stopped, so that high-frequency block 61 is in anon-operating state to reduce and the leakage of interferer tosubsequent circuitry is reduced. After the offset voltage calibrationoperation is completed, a bias is supplied from power supply 62 tohigh-frequency block 61 to set high-frequency block 61 in an operatingstate, and therefore the output impedance of high-frequency block 61fluctuates compared to the time of calibration operation. Meanwhile, theamount of local oscillation signal leaked to the input terminal ofquadrature demodulator 64 and then reflected toward quadraturedemodulator 64 changes, and the fluctuation of the offset voltage at theoutput terminal of quadrature demodulator 64, that is, the residualoffset voltage caused by the variation in the amount of mixing, isgenerated. This conventional example is intended to stabilize the outputimpedance of high-frequency block 61 which differs between the time ofcalibration operation and the time of reception operation, andsuppresses the above residual offset voltage by connecting impedancecompensation block 65 between high-frequency block 61 and quadraturedemodulator 64.

Furthermore, there is still another conventional offset voltagecalibration scheme, whereby in order to restrain the residual offsetvoltage caused by the difference in the operating state of ahigh-frequency block between the time of calibration operation and thetime of reception operation, a dummy circuit having the same circuitconfiguration as a low noise amplifier is provided additionally, one ofthe circuits is set in an operating state and the other circuit is setin a non-operating state during both the time of calibration operationand the time of reception operation, and the reflection coefficientbetween the low noise amplifier and the quadrature demodulator isthereby stabilized (see, for example, Patent Document 4).

FIG. 4 shows conventional reception apparatus 80. In FIG. 4, receptionapparatus 80 is constructed of: low noise amplifier 81 that amplifies areceived signal; dummy low noise amplifier (hereinafter “dummy LNA”) 82that separates an input terminal from an outside terminal to which areceived signal is input; antenna 83; bandpass filter 84; referencecurrent generation circuit 85; and quadrature demodulator 86 thatimplements frequency transformation to a baseband frequency band.

Low noise amplifier 81 is set in a non-operating state during the offsetvoltage calibration operation and low noise amplifier 81 is in anoperating state during the reception operation after the calibrationoperation is completed, and resistance to interferer during thecalibration operation is thereby improved. Here, in order to stabilizethe output impedance of low noise amplifier 81 that differs between thetime of calibration operation and the time of reception operation, theoutput terminal of dummy LNA 82 is connected to a connection midpointbetween the output terminal of low noise amplifier 81 and the inputterminal of quadrature demodulator 86 and the next operation switchingis performed. That is, the residual offset voltage is suppressed bysetting low noise amplifier 81 in a non-operating state and dummy LNA 82in an operating state during the calibration operation, while settinglow noise amplifier 81 in an operating state and dummy LNA 82 in anon-operating state during the reception operation.

Here, restraining the degradation in reception sensitivity requireshighly accurate offset voltage calibration. Furthermore, the basicoperation (operating mode) of the reception apparatus shifts from anidle mode (standby mode), to a start-up mode of starting a referencecurrent circuit and a local oscillator of each reception section, andthen, after a gain setting is performed by again setting section and anoffset voltage calibration operation is carried out, shifts to areception mode and finally returns to an idle mode. If the offsetvoltage calibration operation can be realized fast, it is possible toshorten the operation time of the reception apparatus—that is, extendthe standby time. Therefore, the offset voltage needs to be calibratedfast. On the other hand, when a filter with a large time constant existsin a feedback loop of the calibration circuit, delay is produced in thefilter section, making it difficult to implement high-speed calibration.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-211098Patent Document 2: Japanese Patent Application Laid-Open No. 2000-92143Patent Document 3: Japanese Patent Application Laid-Open No. 2001-245007Patent Document 4: Japanese Patent Application Laid-Open No. 2002-217769DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, in the case of FIG. 1, the conventional apparatus reduces thetime constant of low pass filter 13 during the offset voltagecalibration operation, so that it is possible to make the offset voltagecalibration operation fast. However, since the attenuation of interfererat low pass filter 13 cannot be anticipated, there is a problem thatanalog baseband circuit 17 is saturated and reception sensitivitydegrades.

Furthermore, in the case of FIG. 2, the conventional apparatusattenuates interferer using a forward separation operation in anon-operating state of mixer 37, so that it is possible to improveresistance to interferer. However, since the operating state of mixer 37differs between the time of reception operation and the time of offsetvoltage calibration, there is a problem of producing a residual offsetvoltage.

Furthermore, in the case of FIG. 3, the conventional apparatusattenuates interferer using a forward separation operation in anon-operating state of high-frequency block 61 during offset voltagecalibration, and therefore it is possible to improve resistance tointerferer, and, by adding impedance compensation block 65, reduce theresidual offset caused by the operating state of high-frequency block61, which differs between the reception operation time and offsetvoltage calibration time. However, because it adds circuitry that is notindispensable to the reception operation, there is a problem of causingnoise characteristic degradation at the receiver.

Furthermore, in the case of FIG. 4, the conventional apparatusattenuates interferer using a forward separation operation in anon-operating state of low noise amplifier 81 during the offset voltagecalibration operation, and therefore it is possible to improveresistance to interferer and it is possible to reduce the remainingoffset caused by the operating state of low noise amplifier 81 whichdiffers between the reception operation time and offset voltagecalibration operation time using dummy LNA 82. However, because it addscircuitry that is not indispensable to the reception operation, there isa problem that the noise characteristic of the receiver degrades.Furthermore, because the input terminal of dummy LNA 82 is separatedfrom the outside terminal to which the received signal is input, thereis a problem that it is not possible to completely calibrate theresidual offset voltage caused by the reflected signal of a localoscillation signal leaked out of the semiconductor integrated circuit.

It is therefore an object of the present invention to provide areception apparatus and reception method whereby offset voltagecalibration can be carried out fast and with high accuracy even in anenvironment in which interferer exist, without causing degradation ofnoise characteristics.

Means for Solving the Problem

The reception apparatus according to the present invention comprises anamplification section that carries out processing of amplifying areceived signal, a frequency conversion section that carries outprocessing of converting the frequency of the received signal amplifiedby the amplification section from a radio frequency to a baseband whichis a lower frequency than the radio frequency, a gain control sectionthat amplifies the received signal whose frequency has been converted bythe frequency conversion section at a predetermined gain in dividedstages of a first stage and a second stage, a voltage calibrationsection that performs calibration processing on an offset voltage of thereceived signal generated in the first stage and the second stage duringthe amplification by the gain control section in order from the firststage to the second stage, a filter section that lets pass the receivedsignal in a predetermined band with any one of a first time constant anda second time constant which is reduced from the first time constant ineach of the stages, a time constant control section that sets the timeconstant of the filter section as the second time constant before thecalibration processing for each stage of the calibration processing andchanges the time constant of the filter section included in the stage inwhich the calibration processing is completed in order from the secondtime constant to the first time constant, and an operation controlsection that stops the operation of the amplification section or thefrequency conversion section during the calibration processing in thefirst stage and causes the amplification section or the frequencyconversion section to operate after the calibration processing in thefirst stage is completed and before the calibration processing in thesecond stage.

The reception method of the present invention comprises a step ofperforming processing of amplifying a received signal, a step ofperforming processing of converting the frequency of an amplifiedreceived signal from a radio frequency to a baseband which is a lowerfrequency than the radio frequency, a step of performing gain controlwith such a gain that the received signal whose frequency has beenconverted has predetermined reception quality, a step of performingcalibration processing on an offset voltage of the received signalgenerated during gain control, a step of setting a first time constantduring a reception operation and sets a second time constant which isreduced from the first time constant during calibration processing, astep of letting pass the received signal of a predetermined band withthe set first time constant or the second time constant, and a step ofstopping the operation of amplifying the received signal or theoperation of frequency conversion of the received signal during thecalibration processing and controlling the operation of theamplification processing or operation of performing frequency conversionso as to reduce the offset voltage caused by the switching of theoperation of amplifying the received signal or the operation ofperforming frequency conversion of the received signal.

The semiconductor integrated circuit apparatus of the present inventioncomprises an amplification circuit that performs processing ofamplifying a received signal, a frequency conversion circuit thatperforms processing of converting the frequency of the received signalamplified by the amplification circuit from a radio frequency to abaseband which is a lower frequency than the radio frequency, a gaincontrol circuit that performs gain control with such a gain that thereceived signal whose frequency has been converted by the frequencyconversion circuit has predetermined reception quality, a voltagecalibration circuit that performs calibration processing at an offsetvoltage of the received signal generated during gain control by the gaincontrol circuit, a time constant control circuit that sets a first timeconstant during a reception operation and sets a second time constantwhich is reduced from the first time constant when the voltagecalibration circuit carries out the calibration processing, a filtercircuit that lets pass the received signal of a predetermined band withthe first time constant or the second time constant set by the timeconstant control circuit, and an operation control circuit that stopsthe operation of the amplification circuit that amplifies the receivedsignal or the frequency conversion circuit that performs the frequencyconversion of the received signal during the calibration processing andcontrols the operation of the amplification circuit or the frequencyconversion circuit so as to reduce the offset voltage caused by stoppingthe operation of the amplification circuit or the frequency conversioncircuit.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the present invention, it is possible to perform offsetvoltage calibration fast and with high accuracy even in an environmentin which interferer exist, without causing degradation of noisecharacteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionalreception apparatus;

FIG. 2 is a block diagram showing the configuration of a conventionalreception apparatus;

FIG. 3 is a block diagram showing the configuration of a conventionalreception apparatus;

FIG. 4 is a block diagram showing the configuration of a conventionalreception apparatus;

FIG. 5 is a block diagram showing the configuration of a receptionapparatus according to Embodiment 1 of the present invention;

FIG. 6 is a flow chart showing the operation of the reception apparatusaccording to Embodiment 1 of the present invention;

FIG. 7 is a block diagram showing the configuration of a receptionapparatus according to Embodiment 2 of the present invention;

FIG. 8 is a flow chart showing the operation of the reception apparatusaccording to Embodiment 2 of the present invention;

FIG. 9 is a block diagram showing the configuration of a receptionapparatus according to Embodiment 3 of the present invention;

FIG. 10 is a block diagram showing the configuration of a receptionapparatus according to Embodiment 4 of the present invention; and

FIG. 11 is a block diagram showing the configuration of a receptionapparatus according to Embodiment 5 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

Embodiment 1

FIG. 5 is a block diagram showing the configuration of receptionapparatus 100 according to of Embodiment 1 of the present invention. Lownoise amplifier 101, capacitor 102, quadrature demodulator 103 and phaseshifter 104 constitute high-frequency circuit 114. Variable gainamplifier 105 a, low pass filter 106 a and variable gain amplifier 107 aconstitute analog baseband circuit 115 a. Furthermore, variable gainamplifier 105 b, low pass filter 106 b and variable gain amplifier 107 bconstitute analog baseband circuit 115 b. Furthermore, mixer 103 a andmixer 103 b constitute quadrature demodulator 103, which is ademodulation section.

Low noise amplifier 101 amplifies a received signal and outputs theresult to mixer 103 a and mixer 103 b of quadrature demodulator 103through capacitor 102. Furthermore, low noise amplifier 101 is in anoperating state for amplifying the received signal or in a non-operatingstate for suppressing the received signal, depending on the control ofoperation control circuit 113 during the offset voltage calibrationoperation.

Mixer 103 a converts the frequency of the received signal input from lownoise amplifier 101 through capacitor 102 from a radio frequency to abaseband, and outputs the result to variable gain amplifier 105 a ofanalog baseband circuit 114 a. Furthermore, mixer 103 a is in anoperating state for converting the frequency of the received signal froma radio frequency to a baseband or in a non-operating state forsuppressing the received signal and stopping the processing ofconverting the frequency of the received signal from a radio frequencyto a baseband, depending on the control of operation control circuit 113during the offset voltage calibration operation.

Mixer 103 b converts the frequency of the received signal input from lownoise amplifier 101 through capacitor 102 from a radio frequency to abaseband, and outputs the result to variable gain amplifier 105 b ofanalog baseband circuit 114 b. Furthermore, mixer 103 b is in anoperating state for converting the frequency of the received signal froma radio frequency to a baseband or in a non-operating state forsuppressing the received signal and stopping the processing ofconverting the frequency of the received signal from a radio frequencyto a baseband, depending on the control of operation control circuit 113during offset voltage calibration. When mixers 103 a, 103 b are in anoperating state, quadrature demodulator 103 is also in an operatingstate. When mixers 103 a, 103 b are in a non-operating state, quadraturedemodulator 103 is also in a non-operating state.

Phase shifter 104 generates two signals having a phase difference of 90degrees from each other from the local oscillation signal that is inputfrom a local oscillation source (not shown), and outputs the signals tomixer 103 a and mixer 103 b of quadrature demodulator 103, respectively.

Variable gain amplifier 105 a is a gain control section and calibratesthe offset voltage of the received signal input from mixer 103 a basedon the control of voltage calibration circuit 111. Furthermore, variablegain amplifier 105 a amplifies the received signal input from mixer 103a by a predetermined gain according to an instruction from digitalsignal processing section 108, and outputs the amplified signal to lowpass filter 106 a.

Variable gain amplifier 105 b is a gain control section and calibratesthe offset voltage of the received signal input from mixer 103 b basedon the control of voltage calibration circuit 111. Furthermore, variablegain amplifier 105 b amplifies the received signal input from mixer 103b by predetermined gain according to an instruction from digital signalprocessing section 108, and outputs the amplified signal to low passfilter 106 b.

Low pass filter 106 a is a filter section that lets pass onlypredetermined low frequency of the received signal that is input fromvariable gain amplifier 105 a based on the control of time constantcontrol circuit 110, and thereby eliminates unnecessary components suchas interferer, and outputs the result to variable gain amplifier 107 a.

Low pass filter 106 b is a filter section and lets pass onlypredetermined low frequency of the received signal that is input fromvariable gain amplifier 105 b based on the control of time constantcontrol circuit 110, and thereby eliminates an unnecessary componentssuch as interferer, and outputs the result to variable gain amplifier107 b.

Variable gain amplifier 107 a is a gain control section and calibratesthe offset voltage of the received signal input from low pass filter 106a based on the control of voltage calibration circuit 111. Furthermore,variable gain amplifier 107 a amplifies the received signal input fromlow pass filter 106 a by a predetermined gain according to aninstruction from digital signal processing section 108, and output theamplified signal to digital signal processing section 108.

Variable gain amplifier 107 b is a gain control section and calibratesthe offset voltage of the received signal input from low pass filter 106b based on the control of voltage calibration circuit 111. Furthermore,variable gain amplifier 107 b amplifies the received signal input fromlow pass filter 106 b by a predetermined gain according to aninstruction from digital signal processing section 108 and output theamplified signal to digital signal processing section 108.

Digital signal processing section 108 is a gain setting section andrecovers the data signal from the received signal input from variablegain amplifier 107 a and variable gain amplifier 107 b, and displaysdata on a display section (not shown) or performs audio output to aspeaker (not shown). Furthermore, digital signal processing section 108sets such a gain that the received signals input from variable gainamplifier 107 a and variable gain amplifier 107 b satisfy predeterminedreception quality, controls variable gain amplifier 105 a, variable gainamplifier 105 b, variable gain amplifier 107 a and variable gainamplifier 107 b so that the received signal has the set gain, andoutputs gain information, which is information about the set gain, tosecond decoder 112. Furthermore, digital signal processing section 108outputs a control start signal, which indicates the start of the offsetvoltage calibration of the received signal at a predetermined time, tofirst decoder 109 and second decoder 112.

When a control start signal is input from digital signal processingsection 108, first decoder 109 outputs a calibration start signal tovoltage calibration circuit 111 to start the offset voltage calibrationoperation of the received signal and outputs a time constant controlstart signal, which instructs time constant control circuit 110 toperform operation, to time constant control circuit 110.

Time constant control circuit 110 is a time constant control section andcontrols the time constant to be set in low pass filter 106 a and lowpass filter 106 b based on the time constant control start signal inputfrom first decoder 109.

When a control start signal is input from first decoder 109, voltagecalibration circuit 111 controls variable gain amplifier 105 a, variablegain amplifier 105 b, variable gain amplifier 107 a and variable gainamplifier 107 b to start the offset voltage calibration operation of thereceived signal.

When a control start signal is input from digital signal processingsection 108, second decoder 112 compares the gain in gain informationinput from digital signal processing section 108 with a threshold (firstthreshold). Then, when the set gain is equal to or above the threshold,second decoder 112 outputs an operation control start signal forstopping the operation of low noise amplifier 101 or quadraturedemodulator 103 to operation control circuit 113, and, when the set gainis less than the threshold, second decoder 112 outputs an operationcontrol start signal not stopping the operation of low noise amplifier101 and quadrature demodulator 103, to operation control circuit 113.

When an operation control start signal stopping the operation of lownoise amplifier 101 or quadrature demodulator 103 is input from seconddecoder 112, operation control circuit 113 performs such control as tostop the operation of low noise amplifier 101 or quadrature demodulator103. When an operation control start signal not stopping the operationof low noise amplifier 101 or quadrature demodulator 103 is input fromsecond decoder 112, operation control circuit 113 performs no controlover low noise amplifier 101 and quadrature demodulator 103.

Next, the operation of reception apparatus 100 will be explained usingFIG. 6. FIG. 6 shows a time chart of the control operation by receptionapparatus 100. FIG. 6 shows time waveform #201 of a control start signalwhich is output from digital signal processing section 108, timewaveform #202 of a time constant control start signal which is outputfrom first decoder 109, time waveform #203 of a calibration start signalwhich is output from first decoder 109, time waveform #204 of anoperation control start signal which is output from second decoder 112when the set gain is equal to or above a threshold and time waveform#205 of an operation control start signal which is output from seconddecoder 112 when the set gain is less than the threshold. Furthermore,in FIG. 6, time to time t1 is start-up mode period #206 of receptionapparatus 100, time t1 to time t8 is offset voltage calibration period#207 which is the period during which an offset voltage calibrationoperation of received signal 100 is performed and the period from timet8 onward is reception mode period #208.

Control start signal #209 is output from digital signal processingsection 108 at time t1 after start-up mode period #206 of receptionapparatus 100, which becomes a trigger to start offset voltagecalibration period #207.

When the set gain is equal to or above the threshold, second decoder 112that has received a control start signal outputs operation control startsignal #210 at time t2. Operation control circuit 113 receivingoperation control start signal #210 for the first time sets low noiseamplifier 101 or quadrature demodulator 103 constituting high-frequencycircuit 114 in a non-operating state and reduces the leakage ofinterferer. First decoder 109 that receiving a control start signalsimultaneously with second decoder 112 next transmits time constantcontrol start signal #211 at time t3. Time constant control circuit 110receiving time constant control start signal #211 for the first timereduces the time constant (first time constant) of low pass filters 106a, 106 b which is a predetermined value during start-up period #206 ofreception apparatus 100, set a new time constant (second constant) andreduces a propagation delay, thereby improving the response speed of theoffset voltage calibration of the received signal. By changing the timeconstant in this way, the attenuation characteristic of the receivedsignal at low pass filters 106 a, 106 b during the offset voltagecalibration operation becomes more moderate than the attenuationcharacteristic of the received signal at low pass filters 106 a, 106 boutside the time of the offset voltage calibration operation.

After that, first decoder 109 outputs calibration start signal #212 attime t4. Voltage calibration circuit 111 receiving calibration startsignal #212 for the first time executes the calibration operation. Afterthat, after receiving calibration start signal #213 at time t5 for asecond time in succession, voltage calibration circuit 111 stops thecalibration operation and maintains calibrated data.

Next, time constant control start signal #214 is output from firstdecoder 109 at time t6 for a second time. Time constant control circuit110 receiving time constant control start signal #214 returns the timeconstant of low pass filters 106 a, 106 b to the predetermined value(first time constant). By changing the time constant in this way, theattenuation characteristic of the received signal of low pass filters106 a, 106 b after the offset voltage calibration operation is completedbecomes steeper than the attenuation characteristic of the receivedsignal at low pass filters 106 a, 106 b during the time of the offsetvoltage calibration operation.

After that, operation control start signal #215 is output from seconddecoder 112 at time t7 for a second time. Operation control circuit 113receiving operation control start signal #215 switches the configurationcircuit of high-frequency circuit 114, which was set in a non-operatingstate when operation control start signal #210 was received for thefirst time, to an operating state.

The timing for reducing the time constant of low pass filters 106 a, 106b during offset voltage calibration period #207, the timing forreturning this time constant to the predetermined value, the timing forsetting the operating state of high-frequency circuit 114 to anon-operating state and the timing for returning high-frequency circuit114 in the non-operating state to the operating state are shown in FIG.6, but the underlying concept is as follows.

First, there is a possibility that the circuit may be saturated becauseit is not possible to attenuate interferer when the time constant of lowpass filters 106 a, 106 b is reduced. Therefore, interferer areattenuated by setting the configuration circuit of high-frequencycircuit 114 in a non-operating state before the time constant of lowpass filters 106 a, 106 b is reduced or concurrently with the reductionof the time constant of low pass filters 106 a, 106 b.

Next, when the configuration circuit of high-frequency circuit 114 isreturned from the non-operating state to the operating state, interferercannot be suppressed, and therefore the time constant of low passfilters 106 a, 106 b is returned to the predetermined value before theoperation switching of high-frequency circuit 114 or concurrently withthe operation switching of high-frequency circuit 114.

In FIG. 6, a time difference is provided between the switching of thetime constant of low pass filters 106 a, 106 b and the operationswitching of high-frequency circuit 114, but it is obvious that both canbe performed simultaneously.

Next, when the set gain is less than the threshold, even if seconddecoder 112 receives control start signal #209 as shown in time waveform#205, second decoder 112 does not output an operation control startsignal, and therefore operation control circuit 113 does not switch theoperation of high-frequency circuit 114 and keeps high-frequency circuit114 in an operating state until an idle mode is set once again afterreception apparatus 100 is started. By so doing, the stabilizationperiod required after the switching of the time constants of low passfilters 106 a, 106 b can be shortened.

Therefore, when the set gain is less than a threshold, by delaying thetiming for transmitting control start signal #209 compared to the casewhere the set gain is equal to or above the threshold and delaying thetiming for the start of start-up period #206 of reception apparatus 100,it is possible to shorten offset voltage calibration period #207, thatis, the operation time of reception apparatus 100.

The reason for setting high-frequency circuit 114 in an operating stateor a non-operating state according to the set gain is that, when the setgain is equal to or above the threshold, the desired frequency componentof reception apparatus 100 forms a weak electric field, and there is apossibility that reception apparatus 100 receives interferer at higherlevels than the level of the desired frequency component, and, in thiscase, reception apparatus 100 may saturate unless high-frequency circuit114 is set in a non-operating state to increase the amount ofattenuation. On the other hand, when the set gain is less than thethreshold, the level of the desired frequency component is high andreception apparatus 100 never saturates due to interferer.

In offset voltage calibration period #207, the threshold for determiningwhether or not to switch the operation of high-frequency circuit 114depends on the 1[dB] gain compression point, which becomes a standardfor the linearity of analog baseband circuits 115 a, 115 b and the levelof interferer at the time of interfering wave testing specified for eachradio system, and is set upon designing the circuit so that the circuitis not saturated.

In this way, according to this Embodiment 1, when the set gain is equalto or above the threshold—that is, the reception field intensity ofinterferer input from high-frequency circuit 114—is by far greater thanthe desired received signal, and, only when there is a possibility thatthe receiver may be saturated by interferer in offset voltagecalibration period #207, is the operation of high-frequency circuit 114such as low noise amplifier 101 or quadrature demodulator 103 stopped.On the other hand, when the set gain is less than a threshold—that is,when there is no possibility that the receiver may be saturated byinterferer input from high-frequency circuit 114 in offset voltagecalibration period #207—the operating state of the high-frequencycircuit 114 such as low noise amplifier 101 or quadrature demodulator103 is not changed before or after offset voltage calibration period#207 but is kept in an operating state. By this means, the offsetvoltage can be calibrated with high accuracy even in an environment inwhich interferer exist and the offset voltage can be calibrated fast byshortening the convergence time of transient response from anoperation-stopped state to an operating state of high-frequency circuit114. Furthermore, according to this Embodiment 1, no circuitry that isnot indispensable to the reception operation is added to the paththrough which the received signal passes, and therefore the offsetvoltage can be calibrated fast and with high accuracy even in anenvironment in which interferer exist without causing noisecharacteristic degradation at the receiver.

According to Embodiment 1, although the operation of low noise amplifier101 or quadrature demodulator 103 is stopped during the offset voltagecalibration operation, it is equally possible to stop the operation ofan arbitrary circuit part which is in the path through which thereceived signal in high-frequency circuit 114 passes. Furthermore,according to Embodiment 1, although high-frequency circuit 114 is in anoperating state during the period from start-up mode period #206 untiloperation control circuit 113 receives operation control start signal#210 for the first time, high-frequency circuit 114 may also be set in anon-operating state and may be started after operation control startsignal #215 is received for a second time.

Embodiment 2

FIG. 7 is a block diagram showing the configuration of receptionapparatus 300 according to of Embodiment 2 of the present invention.

Reception apparatus 300 according to this Embodiment 2 corresponds to:reception apparatus 100 according to of Embodiment 1 shown in FIG. 5with second decoder 112 removed, as shown in FIG. 7; detection section310 and decision section 313 added; variable gain amplifiers 301 a, 301b, low pass filters 302 a, 302 b, variable gain amplifiers 303 a, 303 band low pass filters 304 a, 304 b included instead of variable gainamplifiers 105 a, 105 b, low pass filters 106 a, 106 b and variable gainamplifiers 107 a, 107 b; first voltage calibration circuit 306, firsttime constant control circuit 307, second voltage calibration circuit308 and second time constant control circuit 309 included instead oftime constant control circuit 110; and voltage calibration circuit 111and first decoder 305 included instead of first decoder 109. In FIG. 7,the same components as those in FIG. 5 are assigned the same referencenumerals and explanations thereof will be omitted.

Variable gain amplifier 301 a and low pass filter 302 a constitute firststage circuit 314 a. Variable gain amplifier 301 b and low pass filter302 b constitute first stage circuit 314 b. Variable gain amplifier 303a and low pass filter 304 a constitute second stage circuit 315 a.Variable gain amplifier 303 b and low pass filter 304 b constitutesecond stage circuit 315 b. First stage circuit 314 a and second stagecircuit 315 a constitute analog baseband circuit 316 a. First stagecircuit 314 b and second stage circuit 315 b constitute analog basebandcircuit 316 b. Analog baseband circuits 316 a, 316 b perform gaincontrol and offset voltage calibration in a plurality of stages. Offsetvoltage calibration is performed sequentially from earlier circuit tolater circuit, and, with regard to circuits included in the same stagecircuit, calibration is performed sequentially from circuits that areclosest to quadrature demodulator 103.

Digital signal processing section 108 recovers the data signal from areceived signal input from low pass filter 304 a and low pass filter 304b, and displays data on a display section (not shown) or outputs anaudio signal to a speaker (not shown). Furthermore, digital signalprocessing section 108 sets such a gain that the received signal inputfrom low pass filter 304 a and low pass filter 304 b satisfiespredetermined reception quality, controls variable gain amplifier 301 a,variable gain amplifier 301 b, variable gain amplifier 303 a andvariable gain amplifier 303 b such that the received signal has the setgain, and outputs gain information, which is information about the setgain, to decision section 313. Furthermore, digital signal processingsection 108 outputs a control start signal, which indicates the start ofthe offset voltage calibration of the received signal, to first decoder305 and decision section 313 at a predetermined time.

When an operation control start signal stopping the operation of lownoise amplifier 101 or quadrature demodulator 103 is input from decisionsection 313, operation control circuit 113 performs such control as tostop the operation of low noise amplifier 101 or quadrature demodulator103. When an operation control start signal not stopping the operationof low noise amplifier 101 and quadrature demodulator 103 is input fromdecision section 313, operation control circuit 113 performs no controlover low noise amplifier 101 and quadrature demodulator 103.

Variable gain amplifier 301 a is a gain control section and calibratesthe offset voltage of the received signal input from quadraturedemodulator 103 based on the control of first voltage calibrationcircuit 306. Furthermore, variable gain amplifier 301 a performs gaincontrol such that the received signal input from quadrature demodulator103 is set to a predetermined gain according to an instruction fromdigital signal processing section 108 and outputs the signal to low passfilter 302 a.

Variable gain amplifier 301 b is a gain control section and calibratesthe offset voltage of the received signal input from quadraturedemodulator 103 based on the control of first voltage calibrationcircuit 306. Furthermore, variable gain amplifier 301 b performs gaincontrol such that the received signal input from quadrature demodulator103 is set to a predetermined gain according to an instruction fromdigital signal processing section 108 and outputs the signal to low passfilter 302 b.

Low pass filter 302 a is a filter section and removes unnecessarycomponents such as interferer by letting pass only predetermined lowfrequency of the received signal input from variable gain amplifier 301a based on the control of first time constant control circuit 307, andoutputs the result to variable gain amplifier 303 a.

Low pass filter 302 b is a filter section and removes unnecessarycomponent such as interferer by letting pass only predetermined lowfrequency of the received signal input from variable gain amplifier 301b based on the control of first time constant control circuit 307, andoutputs the result to variable gain amplifier 303 b.

Variable gain amplifier 303 a is a gain control section and calibratesthe offset voltage of the received signal input from low pass filter 302a based on the control of second voltage calibration circuit 308.Furthermore, variable gain amplifier 303 a performs gain control suchthat the received signal input from low pass filter 302 a is set to apredetermined gain according to an instruction from digital signalprocessing section 108, and outputs the signal to a low pass filter 304a.

Variable gain amplifier 303 b is a gain control section and calibratesthe offset voltage of the received signal input from low pass filter 302b based on the control of second voltage calibration circuit 308.Furthermore, variable gain amplifier 303 b performs gain control suchthat the received signal input from low pass filter 302 b is set to apredetermined gain according to an instruction from digital signalprocessing section 108, and outputs the signal to low pass filter 304 b.

Low pass filter 304 a is a filter section and removes unnecessarycomponents such as interferer by letting pass only predetermined lowfrequency of the received signal input from variable gain amplifier 303a based on the control of second time constant control circuit 309, andoutputs the result to digital signal processing section 108.

Low pass filter 304 b is a filter section and removes unnecessarycomponents such as interferer by letting pass only predetermined lowfrequency of the received signal input from variable gain amplifier 303b based on the control of second time constant control circuit 309, andoutputs the signal to digital result processing section 108.

When a control start signal is input from digital signal processingsection 108, first decoder 305 outputs a first calibration start signalto first voltage calibration circuit 306 after a predetermined time andalso outputs a second calibration start signal to second voltagecalibration circuit 308. Furthermore, when a control start signal isinput from digital signal processing section 108, first decoder 305outputs a first time constant control start signal to first timeconstant control circuit 307 after a predetermined time and also outputsa second time constant control start signal to second time constantcontrol circuit 309.

First voltage calibration circuit 306 performs control such that offsetvoltage calibration is carried out on variable gain amplifier 301 a andvariable gain amplifier 301 b based on the first calibration startsignal input from first decoder 305, or performs control such thatoffset voltage calibration is stopped.

First time constant control circuit 307 is a time constant controlsection and controls the time constant to adjust the amount ofattenuation at low pass filter 302 a and low pass filter 302 b based onthe first time constant control start signal input from first decoder305.

Second voltage calibration circuit 308 performs control such that offsetvoltage calibration is carried out on variable gain amplifier 303 a andvariable gain amplifier 303 b based on the second control start signalinput from first decoder 305, or performs control such that offsetvoltage calibration is stopped.

Second time constant control circuit 309 is a time constant controlsection and controls the time constant to adjust the amount ofattenuation at low pass filter 304 a and low pass filter 304 b based onthe time constant control start signal input from first decoder 305.

Detection section 310 is provided to monitor the output of quadraturedemodulator 103, measures the received power level of the receivedsignals input from mixer 103 a and mixer 103 b and outputs themeasurement result to decision section 313 as level information.

When a control start signal is input from digital signal processingsection 108, decision section 313 compares the level in the levelinformation input from detection section 310 with a threshold. When thelevel is equal to or above the threshold, decision section 313 decidesthat there exist interferer which become saturation factors of analogbaseband circuits 316 a, 316 b when the amount of attenuation ofinterferer decreases with a reduction in the time constant of low passfilter 302 a and low pass filter 302 b carried out during the offsetvoltage calibration period, and outputs an operation control startsignal stopping the operation of low noise amplifier 101 or quadraturedemodulator 103 of high-frequency circuit 114, to operation controlcircuit 113. On the other hand, when the level is less than thethreshold, decision section 313 decides that there exist no interfererwhich become saturation factors of analog baseband circuits 316 a, 316 bunder the above condition and outputs an operation control start signalnot stopping the operation of low noise amplifier 101 and quadraturedemodulator 103 of high-frequency circuit 114 to operation controlcircuit 113.

Next, the operation of reception apparatus 300 will be explained usingFIG. 8. FIG. 8 is a time chart showing the control operation atreception apparatus 300. FIG. 8 shows time waveform #401 of a controlstart signal which is output from digital signal processing section 108,time waveform #402 of a first time constant control start signal whichis output from first decoder 305, time waveform #403 of a firstcalibration start signal which is output from first decoder 305, timewaveform #404 of a second calibration start signal which is output fromfirst decoder 305 and time waveform #405 of an operation control startsignal which is output from decision section 313. Furthermore, in FIG.8, time t0 to time t10 is start-up mode period #406 of receptionapparatus 300, time t10 to time t20 is offset voltage calibration period#407 which is a period for calibrating the offset voltage of thereceived signal and the period from time t20 onward is reception modeperiod #408.

After start-up mode period #406 of reception apparatus 300, controlstart signal #409 is output from digital signal processing section 108at time t10, which becomes a trigger starting of offset voltagecalibration period #407. Decision section 313 receiving control startsignal #409 compares and decides the level in the level informationinput from detection section 310 with a threshold. Next, decisionsection 313 outputs operation control start signal #410 according to theabove comparison/decision result at time t11.

When it is decided from the comparison/decision result that there existinterferer which become saturation factors of analog baseband circuits316 a, 316 b, operation control start signal #410 stopping the operationof low noise amplifier 101 or quadrature demodulator 103 ofhigh-frequency circuit 114 is output to operation control circuit 113,and operation control circuit 113 receiving operation control startsignal #410 sets low noise amplifier 101 or quadrature demodulator 103constituting high-frequency circuit 114 in a non-operating state,thereby reducing the leakage of interferer. Next, at time t12, firstdecoder 305 outputs first time constant control start signal #411. Firsttime constant control circuit 307 receiving first time constant controlstart signal #411 for the first time reduces the time constant (firsttime constant) of low pass filters 302 a, 302 b, which was apredetermined value during start-up period #406 of reception apparatus300, sets a new time constant (second time constant) and reduces thepropagation delay, thereby improving the response speed of the offsetvoltage calibration operation. By changing the time constant in thisway, the attenuation characteristic of the received signal at low passfilters 302 a, 302 b during the offset voltage calibration operationwith respect to first stage circuits 314 a, 314 b is more moderate thanthe attenuation characteristic of the received signal at low passfilters 302 a, 302 b outside the time of the offset voltage calibrationoperation.

After that, at time t13, first decoder 305 outputs first calibrationstart signal #412. First voltage calibration circuit 306 receiving firstcalibration start signal #412 for the first time executes thecalibration operation on first stage circuits 314 a, 314 b. Then, firstcalibration start signal #413 is output from first decoder 305 for asecond time at time t14. After receiving first calibration start signal#413 for a second time, first voltage calibration circuit 306 stops thecalibration operation and maintains calibration data. By this means, thecalibration processing in the stage (switching stage) of first stagecircuits 314 a, 314 b is completed.

Next, first time constant control start signal #414 is output from firstdecoder 305 for a second time at time t15 after a predetermined time.First time constant control circuit 307 receiving first time constantcontrol start signal #414 returns the time constant of low pass filters302 a, 302 b to the predetermined value (first time constant). Bychanging the time constant in this way, the attenuation characteristicof the received signal at low pass filters 302 a, 302 b with respect tofirst stage circuits 314 a, 314 b after the offset voltage calibrationoperation is completed becomes steeper than the amount of attenuation ofthe received signal at low pass filters 302 a, 302 b during the offsetvoltage calibration operation.

After that, operation control start signal #415 is output from decisionsection 313 for a second time at time t16. Operation control circuit 113receiving operation control start signal #415 sets the configurationcircuit of high-frequency circuit 114 which has been set in anon-operating state by first operation control signal #410 in anoperating state. The convergence time for transient responseaccompanying this operation switching is provided, and, after a steadystate is recovered, first decoder 305 outputs a second time constantcontrol start signal. Second time constant control circuit 309 receivingthe second time constant control start signal for the first time reducesthe time constant (first time constant) of low pass filters 304 a, 304 bwhich was a predetermined value during start-up mode period #406 ofreception apparatus 300, sets a new time constant (second time constant)and reduces the propagation delay, thereby improving the response speedin the offset voltage calibration operation. By changing the timeconstant in this way, the attenuation characteristic of the receivedsignals at low pass filters 304 a, 304 b during the calibrationoperation with respect to second stage circuits 315 a, 315 b becomesmore moderate than the attenuation characteristic of the received signalat low pass filters 304 a, 304 b outside the time of the offset voltagecalibration operation.

Next, first decoder 305 outputs second calibration start signal #416 attime t17. Second voltage calibration circuit 308 receiving secondcalibration start signal #416 for the first time executes thecalibration operation on second stage circuits 315 a, 315 b includingthe remaining offset caused by the switching operation of theconfiguration circuit of high-frequency circuit 114 executed at timet16. Then, at time t18, first decoder 305 outputs second calibrationstart signal #417 for a second time. Second voltage calibration circuit308 receives next second-time second calibration start signal #417 andthen stops the calibration operation and maintains calibration data.With this, the calibration processing in the stage (switching stage) ofsecond stage circuits 315 a, 315 b is completed.

Next, after a predetermined time, first decoder 305 outputs second timeconstant control start signal for a second time. Second time constantcontrol circuit 309 receiving the second time constant control startsignal returns the time constant of lowpass filters 304 a, 304 b to apredetermined value (first time constant). By changing the time constantin this way, the attenuation characteristic at low pass filters 304 a,304 b after the offset voltage calibration operation is completedbecomes steeper than the attenuation characteristic of the receivedsignal at low pass filters 304 a, 304 b during the offset voltagecalibration operation.

After that, decision section 313 outputs operation control start signal#418 at time t19 for a third time. Operation control circuit 113receiving operation control start signal #418 does not change theoperating state of the configuration circuit of high-frequency circuit114.

Next, it is decided from the comparison/decision result that there existno interferer which become saturation factors of analog basebandcircuits 316 a, 316 b, operation control start signal #410 not stoppingthe operations of low noise amplifier 101 and quadrature demodulator 103of high-frequency circuit 114 is output to operation control circuit113, and then, until reception operation period #408, the configurationcircuit of high-frequency circuit 114 is in an operating state. Theoperations of first decoder 305, first voltage calibration circuit 306,first time constant control circuit 307, second voltage calibrationcircuit 308, second time constant control circuit 309 are the same as inthe case where it is decided that there exist interferer, andexplanations thereof will be omitted.

In FIG. 8, a time difference is provided between the switching of thetime constant of low pass filter 302 a, low pass filter 302 b, low passfilter 304 a and low pass filter 304 b and the switching of theoperation of high-frequency circuit 114, but it is obvious that theswitching of the time constant and the switching of the operation can beperformed at the same time.

According to this Embodiment 2, analog baseband circuits 316 a, 316 bare provided in a multi-stage circuit configuration, and offset voltagecalibration is performed in each stage, from earlier circuit,sequentially, while suppressing interferer, and therefore, even ifcorrection differences are caused by the change of the operating stateof high-frequency circuit 114 which has been set in a pause state forsuppression of interferer after the calibration of the earlier stagecircuit is completed, the second stage circuit performs calibrationincluding the above described correction differences, and can therebyrealize calibration of an offset voltage and prevent noisecharacteristic deterioration at reception apparatus 300 since noadditional circuitry such as a dummy LNA or impedance compensation blockfor suppressing the correction differences is used. Furthermore,according to this Embodiment 2, it is decided whether or not receptionapparatus 300 is saturated by interferer before or after the offsetvoltage calibration operation is executed, and, if it is decided thatreception apparatus 300 is not saturated, the operating state ofhigh-frequency circuit 114 is not switched before or after the offsetvoltage calibration operation is executed, so that it is possible toreduce the convergence time for transient response from an operationstopped state to an operating state of high-frequency circuit 114 andimprove resistance against interferer and perform highly accurate offsetvoltage calculation. Furthermore, according to this Embodiment 2, thecircuit which is not indispensable to the reception operation is notadded to the path through which the received signal passes, andtherefore it is possible to calibrate the offset voltage fast and withhigh accuracy even in an environment in which interferer exist withoutcausing any degradation of the noise characteristic of the receiver.

In this Embodiment 2, it is automatically decided by detection section310 and decision section 313 whether or not cases occur where receptionapparatus 300 is saturated before the offset voltage calibrationoperation is executed, but the present invention is not limited to this,and, even if detection section 310 and the function of deciding whetheror not interferer exist from level information input from detectionsection 310 in decision section 313 are removed, it is still possible toset decision criteria for determining whether or not reception apparatus300 saturates at the time of circuit design and fix whether theoperating state of high-frequency circuit 114 is stopped during theoffset voltage calibration operation in each stage of earlier stagecircuit and later stage circuit or whether the operating state is keptor not based on regulations for interferer in the system to whichhigh-frequency circuit 114 is adopted, the gains of the individualcircuits of reception apparatus 300 during normal reception operation,the amount of attenuation under interferer of low pass filters 302 a,302 b, 304 a, 304 b, the level at which an input signal can be blockedwhen high-frequency circuit 114 is in an operation stopped state. Inthis case, even if a correction difference is caused by a change of theoperating state of high-frequency circuit 114, which has been set in apause state for suppression of interferer after the calibration ofearlier stage circuit is completed, later stage circuit performscalibration including correction difference calibration, so that it ispossible to offset voltage calculation of high accuracy and shorten theinterval from time t10 to time t11 required for the automatic decisionfunction.

Furthermore, in this Embodiment 2, although the analog baseband circuithas a two-stage circuit configuration having a first stage circuit and asecond stage circuit, the present invention is not limited to this, andthe analog baseband circuit may adopt a multi-stage configuration withthree or more stages or may not adopt a multi-stage configuration. Whenthe analog baseband circuit adopts a multi-stage configuration, upon thecalibration operation in a stage subsequent to a predetermined stage(switching stage), the time constant for at least one filter in thepredetermined stage or earlier stage than the predetermined stage ischanged to a first time constant, which is increased from a second timeconstant, and the time constant of other filter is set with the secondtime constant. By this means, even if a correction difference is causedby a change of the operating state of high-frequency circuit 114, whichis set in a pause state for suppression of interferer after thecalibration in earlier stage circuit is completed, later stage circuitperforms calibration including the correction difference calibration, sothat it is possible to realize offset voltage calibration of highaccuracy, reduce the time constant of a filter at a position influencingthe calibration operation speed and thereby perform fast and highlyaccurate offset voltage calibration even in an environment in whichinterferer exist, without causing noise characteristic degradation ofthe receiver.

Furthermore, in this Embodiment 2, although the operation of low noiseamplifier 101 and quadrature demodulator 103 is stopped during theoffset voltage calibration operation, the present invention is notlimited to this, and the operation of arbitrary circuit part in the pathin high-frequency circuit 114 where the received signal passes, may bestopped. Furthermore, this Embodiment 2 may also be applied to abovedescribed Embodiment 1. In this case, in FIG. 5, it is possible to adoptanalog baseband circuits 316 a, 316 b in FIG. 7 instead of analogbaseband circuits 115 a, 115 b and make the analog baseband circuit in amulti-stage configuration, and perform offset voltage calibration andtime constant control in each stage as in Embodiment 2. Furthermore, inthis Embodiment 2, high-frequency circuit 114 is set in an operatingstate during the period from start-up mode period #406 until operationcontrol circuit 113 receives first operation control start signal #410,but it is also possible to set high-frequency circuit 114 inanon-operating state and start high-frequency circuit 114 afteroperation control start signal #415 is received for a second time.Furthermore, this Embodiment 2 has explained an example where the timeconstant of low pass filters 302 a, 302 b and low pass filters 304 a,304 b are set to a second time constant during the offset voltagecalibration operation and to a first time constant after the calibrationis completed, but the time constants of low pass filters 302 a, 302 band low pass filters 304 a, 304 b may differ from each other duringtheir respective operations.

Embodiment 3

FIG. 9 is a block diagram showing the configuration of receptionapparatus 500 according to Embodiment 3 of the present invention.

First low noise amplifier 503, second low noise amplifier 504, capacitor505, capacitor 506 and quadrature demodulator 507 constitutehigh-frequency circuit 514. Furthermore, mixer 507 a and mixer 507 bconstitute quadrature demodulator 507, which is a demodulation section.

First bandpass filter 501, corresponding to, for example, a GSM 850 MHzband, lets pass and outputs only a received signal of a predeterminedband, to first low noise amplifier 503.

Second bandpass filter 502, corresponding to, for example, a GSM 900 MHzband, lets pass and outputs only the received signal of a predeterminedband, to second low noise amplifier 504.

First low noise amplifier 503 is an amplification section and amplifiesthe received signal input from first bandpass filter 501 based on thecontrol of operation control circuit 513, and outputs the amplifiedsignal to mixer 507 a and mixer 507 b through capacitor 505.

Second low noise amplifier 504 is an amplification section and amplifiesthe received signal input from second bandpass filter 502 based on thecontrol of operation control circuit 513, and outputs the amplifiedsignal to mixer 507 a and mixer 507 b through capacitor 506.

Mixer 507 a converts the frequency of the received signal input fromcapacitor 505 from a radio frequency to a baseband and outputs thebaseband signal to analog baseband circuit 511.

Mixer 507 b transforms the frequency of the received signal input fromcapacitor 506 from a radio frequency to a baseband and outputs theresult to analog baseband circuit 512.

Phase shifter 508 generates two signals having a phase difference of 90degrees from each other from a local oscillation signal output from alocal oscillation source (not shown), and outputs the signals to mixer507 a and mixer 507 b of quadrature demodulator 507, respectively.

Voltage calibration circuit 509 controls analog baseband circuit 511 soas to calibrate the offset voltage produced in the received signalsubject to gain-control by analog baseband circuit 511.

Voltage calibration circuit 510 controls analog baseband circuit 512 soas to calibrate the offset voltage produced in the received signalsubject to gain-control by analog baseband circuit 512.

Analog baseband circuit 511 calibrates the offset voltage of thereceived signal input from mixer 507 a based on the control of voltagecalibration circuit 509, controls the gain to a predetermined gain, andoutputs the signal to a digital signal processing section (not shown).

Analog baseband circuit 512 calibrates the offset voltage of thereceived signal input from mixer 507 b based on the control of voltagecalibration circuit 510, controls the gain to a predetermined gain, andoutputs the signal to a digital signal processing section (not shown).

When an operation control start signal is input, operation controlcircuit 513 performs such switching control as to operate one of firstlow noise amplifier 503 and second low noise amplifier 504 to which thereceived signal is not input then and stop the operation of the otherone of first low noise amplifier 503 and second low noise amplifier 504to which the received signal is input then.

Next, the operation of reception apparatus 500 in a case where receptionapparatus 500 is receiving a received signal in a GSM 850 MHz band willbe explained as a specific example. Before the offset voltagecalibration operation starts, using an operation control start signalinput from a digital signal processing section (not shown) as a triggersignal, operation control circuit 513 outputs a first operation controlsignal and sets first low noise amplifier 503 in a non-operating state,and outputs a second operation control signal and sets second low noiseamplifier 504 in an operating state. Here, since the service areas ofthe GSM 850 MHz band and the GSM 900 MHz band are not close to eachother, no signal appears at the input terminal of second low noiseamplifier 504 due to the frequency selection effect of second bandpassfilter 502, and, since first low noise amplifier 503 is in anon-operating state and it is possible to suppress interferer whichexist at the input terminal of first low noise amplifier 503, it ispossible to suppress signal power which leaks in later received signalprocessing after quadrature demodulator 507, and improve resistanceagainst interferer.

On the other hand, immediately before a reception mode period after theoffset voltage calibration operation is completed, using an operationcontrol start signal input once again from a digital signal processingsection (not shown) as a trigger signal, operation control circuit 513outputs a first operation control signal to set first low noiseamplifier 503 in an operating state and outputs a second operationcontrol signal to set second low noise amplifier 504 in a non-operatingstate.

In the GSM (Global System for Mobile communications) system, which iswidespread in European and Asian regions (excluding Japan), majorfrequency bands used for the reception system for portable terminalsinclude the GSM 850 MHz band (869 MHz to 894 MHz), GSM 900 MHz band (925MHz to 960 MHz), DCS 1800 MHz band (1805 MHz to 1880 MHz) and PCS 1900MHz band (1930 MHz to 1990 MHz). Generally, the GSM 850 MHz band and GSM900 MHz band, or the DCS 1800 MHz band and PCS 1900 MHz band, are notused in neighboring cells.

To make a reception apparatus supporting to these four bands of the GSMsystem, in consideration of the proximity relationship of the frequencybands with respect to gains in and noise characteristic deviations inthe bands, quadrature demodulator 507 can be shared in the GSM 850 MHzband and GSM 900 MHz band and also in the DCS 1800 MHz band and PCS 1900MHz band. On the other hand, with regard to low noise amplifiers 503,504, the noise characteristic of low noise amplifiers 503, 504 isdominant over the overall noise characteristic of the receptionapparatus, and it is necessary to adopt optimal configuration for eachof the four bands, and therefore it is necessary to adopt aconfiguration that supports the four bands discreetly. Therefore, FIG. 9shows the configuration of high-frequency circuit 514 in realizing, forexample, a dual-band reception apparatus for the GSM 850 MHz band andthe GSM 900 MHz band.

Thus, according to this Embodiment 3, since the low noise amplifier towhich no received signal is input operates, without using additionalcircuitry which becomes a factor for noise characteristic degradation atreception apparatus 500 such as a dummy LNA and impedance compensationblock, even if the operating state of the low noise amplifier foramplification of the received signal differs between the offset voltagecalibration period and the reception mode period, it is possible to keepthe reflection coefficient at the input terminal of the quadraturedemodulator substantially constant and restrain the residual offsetvoltage caused by the self-mixing generated in the quadraturedemodulator. Furthermore, according to this embodiment 3, the inputterminal of each low noise amplifier is connected to the externalterminal outside the semiconductor integrated circuit when thehigh-frequency circuit is integrated, and therefore it is possible tosuppress the residual offset voltage caused by the reflected signal of alocal oscillation signal which leaks out of the integrated circuit, andsecure the amount of attenuation of the received signal during theoffset voltage calibration operation, and thereby perform offset voltagecalibration with high accuracy even in an environment where interfererexist, without causing noise characteristic degradation.

This Embodiment 3 assumes that a received signal in the GSM 850 MHz bandand a received signal in the GSM 900 MHz band are received, but thepresent invention is not limited to this, and the present invention isalso applicable to a case where received signals in different bands arereceived in an arbitrary communication system other than the GSM 850 MHzband and the GSM 900 MHz band.

Embodiment 4

FIG. 10 is a block diagram showing the configuration of receptionapparatus 600 according to Embodiment 4 of the present invention.

Reception apparatus 600 according to this embodiment 4 corresponds toreception apparatus 500 according to Embodiment 3 shown in FIG. 9 withdigital signal processing section 601 and selection section 602 added asshown in FIG. 10. In FIG. 10, the same components as those in FIG. 9 areassigned the same reference numerals and explanations thereof will beomitted.

As assumed in Embodiment 3, FIG. 10 shows the configuration ofhigh-frequency circuit 514 in realizing a dual-band reception apparatusfor the GSM 850 MHz band and the GSM 900 MHz band. Furthermore, as inthe case of Embodiment 3, first low noise amplifier 503 is foramplification of received signals in the GSM 850 MHz band and second lownoise amplifier 504 is for amplification of received signals in the GSM900 MHz band. This embodiment 4 will explain a case where receptionapparatus 600 receives signals in the GSM 850 MHz band, as an example.

Analog baseband circuit 511 calibrates the offset voltage of thereceived signal input from mixer 507 a based on the control of voltagecalibration circuit 509, controls the gain to a predetermined gain, andoutputs the signal to digital signal processing section 601.

Analog baseband circuit 512 calibrates the offset voltage of thereceived signal input from mixer 507 b based on the control of voltagecalibration circuit 510, controls the gain to a predetermined gain, andoutputs the signal to digital signal processing section 601.

Digital signal processing section 601 recovers the data signal from thereceived signal input from analog baseband circuits 511, 512, displaysdata on a display section (not shown) or outputs an audio signal to aspeaker (not shown). Furthermore, digital signal processing section 601outputs information about the radio frequency band used in a nearbycells of reception apparatus 600 (hereinafter “nearby cell information”)out of control channel information included in the data signal toselection section 602.

Selection section 602 stores low noise amplifier selection information(first selection information) which associates information on the radiofrequency band (hereinafter “supported frequency band”) to whichreception apparatus 600 is applicable, with low noise amplifiers 503,504 provided for each supported frequency band. Then, using theproximity cell information input from digital signal processing section601 and with reference to low noise amplifier selection information,selection section 602 selects a low noise amplifier for a band used innearby cells and outputs operation amplifier information during thereception operation to operation control circuit 513, and selects a lownoise amplifier for a band not used in nearby cells and outputsoperation amplifier information during offset voltage calibration, tooperation control circuit 513.

Operation control circuit 513 performs such control as to reduce theoffset voltage caused by stopping the operation of first low noiseamplifier 503 or second low noise amplifier 504. That is, before theoffset voltage calibration operation starts, using an operation controlstart signal input from digital signal processing section 601 as atrigger signal, operation control circuit 513 outputs a first operationcontrol signal and sets first low noise amplifier 503 in a non-operatingstate, and outputs a second operation control signal and sets second lownoise amplifier 504 in an operating state. On the other hand,immediately before the reception mode period after the offset voltagecalibration operation is completed, using the operation control startsignal input again from digital signal processing section 601 as atrigger signal, operation control circuit 513 outputs a first operationcontrol signal and sets first low noise amplifier 503 in an operatingstate, and outputs a second operation control signal and sets second lownoise amplifier 504 in a non-operating state. That is, when selecting alow noise amplifier to operate during the reception mode period and alow noise amplifier to operate during the offset voltage calibrationoperation, based on reception time operation amplifier information andoffset voltage calibration time operation amplifier information,operation control circuit 513 operates the low noise amplifier specifiedby the reception time operation amplifier information during thereception mode period and operates the low noise amplifier specified bythe offset voltage calibration operation amplifier information duringthe offset voltage calibration operation period.

This Embodiment 4 selects a low noise amplifier applicable to thefrequency band farthest from the received signal band in the GSM 850 MHzband and operates the low noise amplifier during the offset voltagecalibration operation, and can thereby restrain saturation in thequadrature demodulator and subsequent circuitry caused by interferer andmisoperation of in the offset voltage calibration operation.

Thus, according to this Embodiment 4, in addition to the advantage ofabove Embodiment 3, it is possible to accurately select the low noiseamplifier to operate during the offset voltage calibration operation.Furthermore, according to this Embodiment 4, a low noise amplifier in aband not used in nearby cells is operated, so that offset voltagecalibration can be performed with high accuracy even in an environmentin which interferer exist.

Embodiment 5

FIG. 11 is a block diagram showing the configuration of receptionapparatus 700 according to Embodiment 5 of the present invention.

Reception apparatus 700 according to this Embodiment 5 corresponds toreception apparatus 500 according to Embodiment 3 shown in FIG. 9 withdigital signal processing section 701, GPS reception apparatus 702 andselection section 703 added, as shown in FIG. 11. In FIG. 11, the samecomponents as those in FIG. 9 are assigned the same reference numeralsand explanations thereof will be omitted.

As assumed in Embodiment 4, FIG. 11 shows the configuration ofhigh-frequency circuit 514 when realizing a dual band receptionapparatus applicable to the GSM 850 MHz band and the GSM 900 MHz band.Furthermore, as in the case of Embodiment 4, first low noise amplifier503 is for amplification of received signals in the GSM 850 MHz band andsecond low noise amplifier 504 is for amplification of received signalsin the GSM 900 MHz band.

This embodiment 5 will explain a method different from the method ofselecting a low noise amplifier to which the received signal is notinput, as explained in Embodiment 4.

A case where reception apparatus 700 receives received signals in theGSM 850 MHz band will be explained as an example.

Analog baseband circuit 511 calibrates the offset voltage of thereceived signal input from mixer 507 a based on the control of voltagecalibration circuit 509, controls the gain to a predetermined gain, andoutputs the signal to digital signal processing section 701.

Analog baseband circuit 512 calibrates the offset voltage of thereceived signal input from mixer 507 b based on the control of voltagecalibration circuit 510, controls the gain to a predetermined gain, andoutputs the signal to digital signal processing section 701.

Digital signal processing section 701 recovers the data signal from thereceived signal input from analog baseband circuits 511, 512 anddisplays the data on a display section (not shown) or outputs an audiosignal to a speaker (not shown).

GPS reception apparatus 702 is mounted on reception apparatus 700 andoutputs position information, which is information about the positionwhere reception apparatus 700 exists, to selection section 703.

Selection section 703 stores low noise amplifier selection information(second selection information) which associates applicable frequencyband information, positional relationship in which an applicablefrequency band is used and a low noise amplifier provided for eachapplicable frequency band. Here, the positional relationship in which anapplicable frequency band is used is, for example, such information thatthe GSM 850 MHz band and PCS 1900 MHz band are mainly used in the U.S.and GSM 900 MHz and DCS 1800 are mainly used in Europe. Using theposition information input from GPS reception apparatus 702 and withreference to the low noise amplifier selection information, a low noiseamplifier for a band used in a proximity cell is selected and receptiontime operation amplifier information is output to operation controlcircuit 513, and a low noise amplifier for a band not used in aproximity cell is selected and offset voltage calibration time operationamplifier information is output to operation control circuit 513. Theoperation of operation control circuit 513 is the same as that of abovedescribed Embodiment 4, and therefore explanations thereof will beomitted.

In this way, according to this Embodiment 5, in addition to theadvantage of above Embodiment 3, it is possible to accurately select thelow noise amplifier to operate during the offset voltage calibrationoperation. Furthermore, according to this Embodiment 5, a low noiseamplifier in a band not used in nearby cells is operated, so that it ispossible to calibrate the offset voltage with high accuracy even in anenvironment in which interferer exist.

Reception apparatuses 100, 300, 500, 600, 700 of above Embodiment 1 toEmbodiment 5 can be made as a semiconductor integrated circuit apparatushaving a circuit configuration (large-scale integrated circuit (LSI)) inwhich circuit configurations such as high-frequency circuits 114, 514are integrated on a single semiconductor substrate.

The present application is based on Japanese Patent Application No.2002-402231, filed on Dec. 1, 2003, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The reception apparatus and the reception method according to thepresent invention provides an advantage of enabling fast and highlyaccurate offset voltage calibration in an environment in whichinterferer exist, without causing any degradation in noisecharacteristics calibration and are useful in offset voltage.

1. A receiving apparatus comprising: an amplification section thatamplifies a received signal; a frequency conversion section thatconverts a frequency of the received signal, amplified by theamplification section, from a radio frequency to a baseband, thebaseband having a lower frequency than the radio frequency, a gaincontrol section that amplifies, by a predetermined gain, the receivedsignal, subjected to the frequency conversion to the baseband, by thefrequency conversion section; a voltage calibration section thatperforms calibration processing on an offset voltage generated in thereceived signal subjected to frequency conversion to the baseband by thefrequency conversion section; a time constant control section that setsa first time constant during a reception operation and sets a secondtime constant, which is reduced with respect to the first time constant,during the calibration processing; a filter section that passes areceived signal of a predetermined band with the first time constant orthe second time constant; and an operation control section that stops anoperation of the amplification section during the calibration processingand controls the amplification section to operate during the receptionoperation, and controls the operation of the amplification section so asto reduce a residual offset voltage caused by switching the operation ofthe amplification section.
 2. The receiving apparatus according to claim1, wherein: the amplification section is provided per received signal ina plurality of different bands and performs amplification processing forthe different bands; and the operation control section, during thecalibration processing of the received signal subjected to frequencyconversion to the baseband by the frequency conversion section, theoperation control section stops the operation of the amplificationsection used for amplification of the received signal, in the band beingsubjected to reception processing, and reduces the offset voltage byperforming switching so as to cause the amplification section used foramplification of the received signal, in the band not being subjected toreception processing, to operate.
 3. The receiving apparatus accordingto claim 2, wherein the operation control section cause theamplification section used for amplification of the received signal inthe band not used in a proximity cell to operate during the calibrationprocessing.
 4. The receiving apparatus according to claim 2, furthercomprising a storage section that stores first selection informationwhich associates a band with the amplification section, wherein theoperation control section selects the amplification section to bestopped and the amplification section to be operated, with reference tothe first selection information using information on the band reportedfrom a communicating party.
 5. The receiving apparatus according toclaim 2, further comprising a storage section that stores secondselection information which associates position information, the bandwith the amplification section, wherein the operation control sectionselects the amplification section to be stopped and the amplificationsection to be operated, with reference to the second selectioninformation using the position information indicating a position of thereceiving apparatus.
 6. The receiving apparatus according to claim 1,wherein: the operation control section stops operation of theamplification section during the calibration processing, when the gain,upon amplification of the received signal by the gain control section,is equal to or more than a threshold value; and the operation controlsection performs switching so as to cause the amplification section tooperate during the calibration processing, when the gain, uponamplification of the received signal by the gain control section, isless than the threshold value,
 7. The receiving apparatus according toclaim 1, further comprising a detection section that detects a level ofreceived power of the received signal subjected to frequency conversionto the baseband by the frequency conversion section, wherein: theoperation control section stops operation of the amplification sectionduring the calibration processing, when the level of the received powerdetected by the detection section is equal to or more than a thresholdvalue: and the operation control section reduces the offset voltage byperforming switching so as to cause the amplification section to operateduring the calibration processing, when the level of the received powerdetected by the detection section is less than the threshold value.